As computer CPUs, graphic cards, transmission means, and other elements and facilities increase in speed and complexity, they become able to handle increasingly greater amounts of data. This is beneficial in that it allows for the execution of more complex tasks in shorter amounts of time, to the benefit of users. However, computer memory is a key resource that often affects machine speed and capabilities, and the advances in other areas cannot be fully effective without concomitant advances in memory capabilities.
One primary measure of the effectiveness of computer memory technologies is memory density. Often this is given in terms of bits per cm2 of materials, or b/cm2. Memory technologies have advanced to the point that memory densities on the order of 62.5 Gb/cm2 are attainable using certain experimental approaches. For example, in “The Nanodrive Project,” by Vettiger et al, Scientific American, page 47 of the January 2003 issue (the identified article being incorporated herein by reference in its entirety without exclusion of any portion thereof), such a memory system is described. The Vettiger memory system employs an array of 4000 cantilevers, each of which can be electrically heated to 400 degrees Celsius and flexed, via the heating effect, to form an imprint in a plastic writing surface. The imprint may be on the order of 40 nm across. Reading the pits thus formed is done by scanning the tips, heated to a lesser temperature than the writing temperature, across the writing surface and recording changes in temperature and electrical impedance caused when a tip encounters a pit. Erasing of data is performed by reheating a tip to the writing temperature and using the hot tip to fill in the pit.
While the Vettiger system allows for fairly high memory densities, there are a number of drawbacks inherent in the system that hamper its use in practical applications. For example, electrically heating the cantilever tips is resource intensive, potentially requiring as much as a watt of power to heat the example array of 4000 tips. In addition, the writing surface may not be completely smoothed by the erase process, causing potential errors on subsequent write/read cycles.
More traditional memory technologies do not suffer the aforementioned power and accuracy limitations, but offer much lower memory density. For example, some of best DRAMs available have densities on the order of 0.05-0.1 Gb/cm2. Moreover, the access time for such memories is relatively slow. While SRAMs are typically faster, they tend to have lower densities. In addition, both DRAMs and SRAMs are typically volatile. Thus a memory technology is needed that offers improved memory density without incurring the costs and limitations discussed above.